An ink jet recording system is a system of forming fine liquid droplets using an aqueous ink and blowing them to a recording medium by various methods to form images. Demand for the ink jet recording system has been increased remarkably in recent years because it does not result in unpleasant odor of an organic solvent due to the use of an aqueous ink, generates less noises and requires low running cost. Particularly, since color printing can be conducted easily in homes, simple printing at a personal level including printing for new year's cards is enabled.
However, the ink jet recording system involves a significant drawback when adopted industrially in that a printing speed is limited. That is, for attaining high speed color printing, a plurality kinds of inks have to be absorbed instantly after the inks have been blown to the recording medium. When the absorbing speed is low, blotting may occur or succeeding ink is blown and mixed before the ink blown precedingly has been absorbed, failing to obtain clear coloring.
In order to improve the ink absorption speed, various proposals have been made for recording paper in which a water absorbing substance is mixed in a coated layer. For example, Japanese Patent Laid-Open No. 34481/1999 discloses recording paper using gelatin material as a binder in a coated layer and Japanese Patent Laid-Open No. 34484/1999 discloses a recording material using a filler of good ink absorption.
However, when the paper is produced by such a coating system, the cost is inevitably increased. Accordingly, for producing high performance ink jet recording paper at a reduced cost, a non-coated type recording paper that can be manufactured in one step not by way of a coating step is desirable.
The non-coated type recording paper is generally marketed as wood free paper type or common paper type. In ink jet recording paper of marketed common paper type, an excessive sizing agent is incorporated in order to overcome spread of letters upon letter printing, which lowers the ink absorption speed. Such recording paper can provide a sufficient performance when used in printing only for the letters by a high speed ink jet printer, but images are blotted failing to obtain clear images when conducting multi-color printing.